Process for the preparation of aromatic dicarboxylic acid dichlorides

ABSTRACT

A one-stage process for the preparation of pure aromatic dicarboxylic acid dichlorides by reacting an aromatic dicarboxylic acid or an aromatic dicarboxylic acid mixture with phosgene, optionally, in a solvent or diluent, with phosphine imines, phosphorimidates or mixtures thereof as catalysts.

This invention relates to a one-stage process for the preparation ofhigh purity polycondensable aromatic dicarboxylic acid dichlorides.

The production of aliphatic and aromatic acid chlorides by the reactionof a carboxylic acid with phosgene has been described in U.S. Pat. Nos.3,184,506; 3,544,626; 3,544,627 and 3,547,960 and in GermanOffenlegungsschrift Nos. 2,400,007 and 2,321,122. The reaction productsobtained from these processes are dark coloured carboxylic acidchlorides which are from 96to 99% pure. Aromatic dicarboxylic aciddichlorides having such a low degree of purity cannot be used directlyin the diphasic interface polycondensation process for the production ofhigh molecular weight polycondensates, such as aromatic polyamides oraromatic polyesters. The presence therein of unreacted or onlysemi-reacted dicarboxylic acids interface with polycondensation, causesunwanted chain breakage and results in polymers containing carboxyl endgroups. The aromatic dicarboxylic acid dichlorides obtained are dark incolour due to the impurities and have an undesirable carbamic acidchloride content resulting from the reaction thereof with catalysts (seeChem. Ref. 1973, Vol. 73, No. 1, page 77 or Angewandte Chemie (1974),Year 1962, No. 21, page 864).

If colourless dicarboxylic acid dichlorides are to be obtained, thecrude products must be purified by recrystallisation or distillation.This requires additional effort and reduces the yield and, in the caseof aromatic dicarboxylic acid dichlorides, there is the risk ofspontaneous decomposition.

The present invention relates to a one-stage process for the preparationof pure aromatic dicarboxylic acid dichlorides by the reaction of anaromatic dicarboxylic acid with phosgene in the presence of a catalystand optionally in a solvent and/or diluent, characterised in that thecatalysts used are phosphine imines or phosphorimidates or mixturesthereof. The aromatic dicarboxylic acid dichlorides obtained arevirtually colourless and apart from the catalysts put into the processcontain 0.1% or less of impurities so that they may be directly used forthe preparation of colourless, high molecular weight polycondensateswithout being first purified.

The phosphine imines or phosphorimidates or mixtures thereof used ascatalysts according to the present invention do not interfere with thesubsequent processes, such as the preparation of aromatic polyesters.The catalysts are separated from the organic polymer solution by theaqueous alkaline phase when the product is subsequently washed by thetwo-phase interface method after polycondensation.

Suitable catalysts according to the present invention include phosphineimines corresponding to general formula (I) and phosphorimidatescorresponding to general formula (II): ##STR1## wherein when z=1, R andB represent C₁ -C₈ alkyl, C₆ -C₁₀ aryl, C₇ -C₂₀ alkylaryl or arylalkyl;

y=0 and x=1 or

y=1 and x=1 when A represents ##STR2## or --SO₂ --; or y=1 and x=2 whenA represents ##STR3## and, when z=2 or 3, A, R, x, and y are as definedabove, but B represents C₆ -C₁₀ aryl or C₇ -C₂₀ alkylaryl.

Phosphine imines or phosphorimidates corresponding to general formulae(III) and (IV) are also suitable catalysts according to the presentinvention: ##STR4## wherein R is as defined above; M represents CH₃ orC₆ H₅ ;

and n,m=1,2 or 3,

and n+m=4.

The following are examples of individual compounds which are suitable:##STR5## wherein R' represents CH₃, C₆ H₅, C₂ H₅ O, CH₃ O or C₆ H₅ O;

D represents CH₃, C₆ H₅, ##STR6## or cyclohexyl; R" represents CH₃, C₆H₅ or C₁₀ H₇ ; and

R'" represents C₆ H₁₃, C₄ F₉, C₆ H₅, ##STR7## CH₃.

Phosphine imines corresponding to general formula (I) or (III) andphosphorimidates corresponding to general formula (II) or (IV) which aresuitable catalysts according to the present invention may be prepared,for example, by the reaction of tertiary phosphines or of phosphiteswith the corresponding azides accompanied by the elimination of nitrogenin accordance with the following reaction scheme (see Kosolapoff, Maier"Organic Phosphorous Compounds", Vol. 3, pages 71-73 and 127-153, andVol. 6, pages 611-612): ##STR8##

The following individual compounds are particularly suitable: ##STR9##

According to the present invention, the phosphine imines orphosphorimidates or mixtures thereof are used in quantities of from 0.1to 3.0%, by weight, preferably from 0.2 to 1.5%, by weight, based on thearomatic dicarboxylic acids used.

Aromatic dicarboxylic acids correspond to the following generalformulae: ##STR10## wherein R represents H, C₁ -C₄ alkyl or halogen(preferably chlorine or bromine);

X represents a single bond, --O--, --S--, --CH₂, ##STR11## or C₅ -C₇cycloalkylene.

Mixtures may also be used.

The following are examples: phthalic acid, isophthalic acid,terephthalic acid, mixtures of iso- and tere-phthalic acid, diphenicacid and 1,4-naphthalene dicarboxylic acid.

The solvent or diluent used is preferably the aromatic dicarboxylic aciddichloride or mixture of aromatic dicarboxylic acid dichlorides formedduring the reaction. Inert diluents, such as aliphatic or aromatichydrocarbons, halogen-substituted aromatic hydrocarbons,halogen-substituted aliphatic hydrocarbons or saturated aliphaticethers, may also be added. The reaction temperature is generally from70° to 180° C., preferably from 100° to 160° C.

The molar ratio of aromatic dicarboxylic acid to phosgene is preferablyfrom 1:2 to 1:2.5, i.e. is advisable to use a slight excess of phosgeneto replace the losses resulting from the expulsion of CO₂ and HCl gasfrom the reaction mixture during phosgenation.

The process according to the present invention may be carried outbatch-wise or continuously. In one continuous embodiment, a solution ofaromatic dicarboxylic dicarboxylic acid dichloride and catalyst flowsdown a reaction tube counter to an upward stream of phosgene gas, andthe aromatic dicarboxylic acid dichloride and catalyst are removed atthe bottom of the reaction tube.

In a batch-wise embodiment, aromatic dicarboxylic acid, aromaticdicarboxylic acid dichloride and catalyst are introduced into a reactionvessel at normal pressure. The reaction mixture is then heated to from140° to 160° C., with stirring, the aromatic dicarboxylic acid partly orcompletely dissolving under these conditions. From 2 to 2.5 mol ofgaseous phosgene per mol of aromatic dicarboxylic acid are introduced atthis temperature.

The residue obtained after removal of excess phosgene, HCl and CO₂ gasby brief application of a vacuum contains ≧99.9% of aromaticdicarboxylic acid dichloride in addition to the quantity of catalystused and may be converted into high molecular weight colourlesspolycondensates without further purification.

EXAMPLE 1

203 g (1 mol) of isophthalic acid dichloride, 166 g of isophthalic acid(1 mol) and 0.8 g of: ##STR12## are heated to 148° C. in around-bottomed flask which is equipped with thermometer and stirrer andwith a condenser which is maintained at -20° C. by means of coolingbrine. Phosgene is introduced at from 148° to 157° C., with stirring,and the mixture is refluxed until the temperature of the reactionmixture falls to 146° C.

After cooling of the reaction mixture to 120° C., a water jet vacuum isapplied to remove excess phosgene, as well as any HCl and CO₂ gasdissolved in the reaction mixture.

Yield: 406.5 g of a colourless residue consisting of 0.8 g of thephosphine imine catalyst put into the process and 405.7 g of a 100%isophthalic acid dichloride (determined by titration).

EXAMPLE 2

101.5 g (0.5 mol) of isophthalic acid dichloride, 101.5 g (0.5 mol) ofterephthalic acid dichloride, 83 g (0.5 mol) of isophthalic acid, 83 g(0.5 mol) of terephthalic acid and 0.8 g of: ##STR13## are reacted withphosgene as described in Example 1.

Yield: 406.8 g of a colourless residue consisting of 0.8 g of thephosphorimidate catalyst put into the process and 406 g of a mixture of100% isophthalic and terephthalic acid dichloride (determinedtitrimetrically).

EXAMPLE 3

101.5 g (0.5 mole) of isophthalic acid dichloride, 101.5 g (0.5 mol) ofterephthalic acid dichloride, 83 g (0.5 mol) of isophthalic acid, 83 g(0.5 mol) of terephthalic acid and 0.8 g of:

    (C.sub.6 H.sub.5).sub.3 P═N--CO--CH.sub.3

are reacted with phosgene as described in Example 1.

Yield: 406 g of 99.9% isophthalic and terephthalic acid dichloride and0.8 g of the phosphine imine catalyst put into the process.

EXAMPLE 4

101.5 g (0.5 mol) of isophthalic acid dichloride, 101.5 g (0.5 mol) ofterephthalic acid dichloride, 83 g (0.5 mol) of isophthalic acid, 83 g(0.5 mol) of terephthalic acid and 0.3 g of catalyst corresponding tothe formula: ##STR14## are reacted with phosgene as described in Example1.

Yield: 406 g of an almost colourless residue of 0.3 g of catalyst and405.7 g of a mixture of 100% isophthalic and terephthalic aciddichloride (determined titrimetrically).

We claim:
 1. A process for preparing an aromatic dicarboxylic aciddichloride which comprises reacting an aromatic dicarboxylic acid withphosgene in the presence of a catalytic amount of at least one phosphineimine or phosphoramidate, said aromatic dicarboxylic acid being selectedfrom the group consisting of ##STR15## and mixtures thereof wherein R ishydrogen, alkyl having 1 to 4 carbon atoms or halogen and --X-- is asingle bond, --O--, --S--, --CH₂ --, ##STR16## or cycloalkylene having 5to 7 carbon atoms.
 2. A process of claim 1 wherein said reaction iscarried out in the presence of a reaction inert diluent.
 3. A process ofclaim 1 wherein said phosphine imine is of the formula ##STR17## andsaid phosphorimidate is of the formula ##STR18## wherein when z equals1, R and B are C₁ -C₈ alkyl, C₆ -C₁₀ aryl, C₇ -C₂₀ alkaryl or C₇ -C₂₀aralkyl; y is 0 and x is 1 or y is 1, x is 1 and A is --CO--, ##STR19##or --SO₂ -- or y is 1, x is 2 and ##STR20## or when z is 2 or 3, A, R, xand y are each as aforesaid and B is C₆ -C₁₀ aryl or C₇ -C₂₀ alkaryl. 4.A process of claim 1 wherein said phosphine imine is of the formula

    (R.sub.3 P=N).sub.m Si(M).sub.n

and said phosphorimidate is of the formula ##STR21## wherein R is C₁ -C₈alkyl, C₆ -C₁₀ aryl, C₇ -C₂₀ alkaryl or C₇ -C₂₀ aralkyl, M is CH₃ or C₆H₅, n and m are each 1, 2 or 3 and n+m is 4.